AC unit feeder and branch circuits NEC 430

[Rob 998]

This subject has been beat almost to death before, but there is one distinction I would like everyone's opinion on.

There is a 12AWG Romex, running 240V (on black and white conductors) from the inside load distribution center on a two pole 30A breaker, feeding the required outside disconnecting means, which happens to be fused with 30A time delay fuses. The circuit feeds a single AC unit in a residential setting.

Does use of the fused disconnect, whether or not it was required to provide the rated OCP per the AC unit that the breaker may or may not meet, constitute the final OCPD and now mean that the line from the distribution center to the outside disconnecting means is a feeder, not a branch circuit, and now no longer exempt from the rules allowing smaller conductors in the branch circuit to the AC unit due to the internal thermal overload protection on the AC compressor motor?

Is this a common practice anyways? How serious of a code violation might this be? Construction of this building is mid 80's, North Carolina, whereby I think the use of white for a non-grounded conductor might have been OK, the main question is the feeder vs. branch distinction.

 

[retirede]

IMO, the fuses are supplemental protection. You do not have a feeder. The 12 GA is compliant as long as the MCA is not more than 20A.

 

[winnie]

It is common practice and not a code violation.

I agree with the OP that the conductors from panel to outside fused disconnect constitute a feeder rather than a branch circuit. However this is a single branch circuit feeder, safely sized following the same rules as for a branch circuit.

The use of a white wire in a cable assembly as an ungrounded conductor is still allowed and is still common practice.

-Jon

 

[Strathead]

IMO, the fuses are supplemental protection. You do not have a feeder. The 12 GA is compliant as long as the MCA is not more than 20A.

Really, and what code do you base that on. The definition of a feeder and a branch circuit are quite clear. The disconnect is part of the building wiring system and the feeder ends in fuses in the disconnect. The AC branch circuit extends from there. You can disagree with the need to run larger wire, but the code requires you to.

 

[Dennis Alwon]

I agree it is a feeder up to the disconnect and a branch circuit to the unit from the fused disconnect. I tried to make a definition to change that but it got rejected. When I asked a panel of cmp members they said they would consider the entire run a branch circuit however the code does not support that.

 

[infinity]

Really, and what code do you base that on. The definition of a feeder and a branch circuit are quite clear. The disconnect is part of the building wiring system and the feeder ends in fuses in the disconnect. The AC branch circuit extends from there. You can disagree with the need to run larger wire, but the code requires you to.

It's been argued that the definition of supplementary overcurrent protection would negate part of this circuit from being a feeder and IMO it should but the definition is far from conclusive. Since this entire circuit is feeding only one piece of equipment there is no reason why the branch circuit shouldn't by definition begin at the panel.

 

[Rob 998]

Thanks for the input so far. I see it still isn't completely agreed upon. To muddy the waters further, let's say the 30A breaker in the main panel does NOT meet the label specifications on the AC unit as required OCP, and this function is performed by the 30A fuses in the disconnect. Does that not make the feeder/branch circuit originating at the main panel if we use the argument that the entire run is a branch circuit, non compliant anyways?

 

[winnie]

Ok, so you have a 30A double pole breaker connected to 12ga NM cable, going to an outside disconnect with 30A fuses, supplying 12ga THHN in sealtite to a minisplit with a label that says something like "18A MCA 30A maximum fuse".

I'd have zero problem with such an installation. You have wires protected at less than the nameplate OCPD, and you have wires with more than the nameplate required ampacity. I would not be fussed at all that some of the wires were feeder and some were branch circuit.

I see @Rob 998 's contention that the 'feeder' portion of this circuit is _not_ protected in accordance with the nameplate as plausibly correct but IMHO not relevant to any actual safety issues. The breaker still provides the necessary short circuit protection for the wires, the fuses provide whatever additional external protection is required by the HVAC unit, and the HVAC unit overload still provides overload protection for the wires.

-Jon

 

[david luchini]

Does use of the fused disconnect, whether or not it was required to provide the rated OCP per the AC unit that the breaker may or may not meet, constitute the final OCPD and now mean that the line from the distribution center to the outside disconnecting means is a feeder, not a branch circuit, and now no longer exempt from the rules allowing smaller conductors in the branch circuit to the AC unit due to the internal thermal overload protection on the AC compressor motor?

Yes, the fused switch is the branch circuit device. No, the feeder portion is not "no longer exempt" from the rules allowing smaller conductors.

 

[don_resqcapt19]

It doesn't make any difference as when you apply the feeder rules to a circuit that supplies a single load, you end up with the same conductor size and OCPD.

 

[augie47]

It doesn't make any difference as when you apply the feeder rules to a circuit that supplies a single load, you end up with the same conductor size and OCPD.

I agree. Art 440 does not address feeders so you have to refer back to Art 430 where 430.62 would allow the 30 amp protection as 440.22 is addressed in 430.62.

 

[infinity]

I agree. Art 440 does not address feeders so you have to refer back to Art 430 where 430.62 would allow the 30 amp protection as 440.22 is addressed in 430.62.

Five code references in one sentence. There has to be a better way to write code than this, like fixing the definition of a feeder when it applies to this type of installation.

 

[jap]

Most of the times I find wire in an outside AC disconnect that doesn't meet the rating of the OCPD located in the panel, I also witness an electrician and his helper high fiving each other on the way back to the truck just after an inspector clarified that what they just did as far as installing a larger OCPD on smaller wire to get the job done wasn't a code violation at all where they weren't completely sure whether it was or not.

Jap>

 

[Little Bill]

I have a question that I've been thinking of. We know the compressor in an AC unit has overload protection, and that is why we can use a larger breaker with smaller conductors. What if the fan motor doesn't have OL protection and it locks up for some reason?

 

[mtnelect]

As a C10, it always didn't seem right to me even though there is an exemption(s). So, I always installed the branch circuit wiring according to the maximum overcurrent device rating. Most of the time I install the unit close to the panel anyway.

Also, I am only installing ductless units anyway that have much lower current draws than conventional condensing units.

 

[mtnelect]

I have a question that I've been thinking of. We know the compressor in an AC unit has overload protection, and that is why we can use a larger breaker with smaller conductors. What if the fan motor doesn't have OL protection and it locks up for some reason?

All condenser fan motors all have thermal overloads imbedded in them.

 

[Eddie702]

Ok, so you have a 30A double pole breaker connected to 12ga NM cable, going to an outside disconnect with 30A fuses, supplying 12ga THHN in sealtite to a minisplit with a label that says something like "18A MCA 30A maximum fuse".

I'd have zero problem with such an installation. You have wires protected at less than the nameplate OCPD, and you have wires with more than the nameplate required ampacity. I would not be fussed at all that some of the wires were feeder and some were branch circuit.

I see @Rob 998 's contention that the 'feeder' portion of this circuit is _not_ protected in accordance with the nameplate as plausibly correct but IMHO not relevant to any actual safety issues. The breaker still provides the necessary short circuit protection for the wires, the fuses provide whatever additional external protection is required by the HVAC unit, and the HVAC unit overload still provides overload protection for the wires.

-Jon

"12 gage THHN to a minisplit" I thought you can't use THHN outdors it is a wet location?

 

[retirede]

"12 gage THHN to a minisplit" I thought you can't use THHN outdors it is a wet location?

I haven’t seen THHN in many years that wasn’t also labeled THWN-2. People just use THHN for a shortcut.

 

[winnie]

"12 gage THHN to a minisplit" I thought you can't use THHN outdors it is a wet location?

You are correct.

I was speaking loosely and should have said THWN. As noted by @retirede I have never seen THHN that wasn't also rated THWN, and used THHN as shorthand for the multi rated product.

Jon

 

[Eddie702]

You are correct.

I was speaking loosely and should have said THWN. As noted by @retirede I have never seen THHN that wasn't also rated THWN, and used THHN as shorthand for the multi rated product.

Jon

Your right. They are all dual rated know. Wasn't always that way.